comparison of retinal image quality between sbk and...

Comparison of Retinal ImageQuality betweenSBK and PRK

Allen Boghossian, D.O.Durrie Vision

Overland Park, KS

Study Design

• Purpose: To compare optical quality and intraocular scatterbetween SBK and PRK using double-pass (DP) technology

• Analysis performed using the Optical Quality AnalysisSystem (OQAS) (Visiometrics SL, Tarrasa, Spain)

• Author has no commercial affiliation with Visiometrics

• 25 patients (50 eyes)– One eye treated with SBK (25 eyes)– Fellow eye treated with PRK (25 eyes)– Subjects randomized according to dominant eye– All SBK flaps made using the 60 Hz IntraLase FS Laser– All eyes treated with wavefront guided Alcon LADAR6000– Average Age: 31 ± 5 years– Mean MRSE:

• SBK eyes: -4.18 ± 1.03 D• PRK eyes: -4.30 ± 1.04 D

– Measurements at pre-op, 1, 3, and 6 months

Study Design

IntroductionWhat is SBK?

Sub-Bowman's Keratomileusis (SBK)

• Corneal flap just below the level of Bowman’s membranecreated by Intralase FS laser

• Optimal flap: 8.5 mm diameter, 100 microns or less,centered on visual axis

• Has advantage of both Lasik and surface ablation• Decreased post-op dryness, decreased loss of sensitivity,

and decreased higher order aberrations

Part of larger SBK vs. PRK comparative study:1. Visual acuity, refractive Outcome2. Corneal sensitivity3. Dry eye signs/symptoms4. Endothelial cell count5. Keratocyte cell density – ARVO 20076. Corneal biomechanical properties – ASCRS 20077. Intraocular pressure comparison:

a. Goldmann Applanation Tonometer (GAT)b. Ocular Response Analyzer (ORA)c. Pascal Dynamic Tonometer (PDT)

8. Wavefront analysis9. Patient questionnaire10. OQAS analysis

Introduction

IntroductionOQAS

Optical Quality Analysis System (OQAS)• Objective measurement of visual quality• Uses double-pass (DP) technology to measure light

reflection from retina including light scatter (LS) and higherorder aberrations (HOA)

IntroductionHow does OQAS work?

1. A motorized optometer lenses correctsfor patient’s defocus

2. First pass, the system sends a diodelaser light (780 nm) into the eye

3. Produces an image of a circular spoton the retina

4. Second pass, the reflection of the spotis measure by a light camera

5. Directly measures the point spreadfunction (PSF) of the optical system

6. Using Fourier analysis, the PSF data istranslated to a modulation transferfunction (MTF) value

7. Measurement at 4mm undilated pupils

Double-Pass Technology

• The main advantage of this instrument compared withaberrometers is that it directly obtains the actual retinalimages including lower, higher order aberrations andintraocular scattering.

• Current aberrometers mathematically calculate MTF values• OQAS measures MTF directly

IntroductionOQAS

• MTF is the square root of the modulus of the Fouriertransformation of the average double-pass image

• Correlates to the loss ofcontrast in the retinal imagefor each spatial frequency

• Average value is 30.0• The higher the MTF value the

higher the quality of image

IntroductionMTF Value

• OQAS numericalmeasurement of contrastsensitivity

• Average value is 1.0• Higher the contrast value the

higher the quality of image

IntroductionContrast Value

ResultsUncorrected Vision – 1 month

0%10%20%30%40%50%60%70%80%90%

100%

20/16 orbetter

20/20 orbetter

20/25 orbetter

20/40 orbetter

SBKPRK

N = 25

64%

28%

80%

44%

88%76%

100% 92%

0%10%20%30%40%50%60%70%80%90%

100%

20/16 orbetter

20/20 orbetter

20/25 orbetter

20/40 orbetter

SBKPRK

N = 25

ResultsUncorrected Vision – 1 month

67%75%

92% 88%100% 100%

0%10%20%30%40%50%60%70%80%90%

100%

20/16 orbetter

20/20 orbetter

20/25 orbetter

20/40 orbetter

SBKPRK

N = 25

ResultsUncorrected Vision – 3 months

ResultsMRSE and Cylinder

-0.38

-0.27

-0.08

-0.17

1 month

-0.40

-0.18

-0.15

-0.12

3 months

-0.61PRK

-0.70SBK

-4.30PRK

-4.18SBK

Pre-OP

MR

SEC

ylin

der

Which Eye Has Better Vision?Through 3 Months

0%10%20%30%40%50%60%70%80%90%

100%

1 Month 3 Months

SBK Better VisionPRK Better VisionBoth Same

N=25

OQASAverage MTF

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

Pre-Op 1 Month 3 Month 6 Month

SBKPRK

N=25

MTF

OQASAverage MTF

30.09 29.39

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00


SBKPRK

N=25

MTF

OQASAverage MTF

30.09 29.3931.85 30.88 29.93

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00


SBKPRK

N=25

MTF

OQASAverage MTF

30.09 29.3931.85

25.61

30.88 29.49 29.9327.81

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00


SBKPRK

N=25

MTF

OQASContrast Value

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40


SBKPRK

N=25

Con

trast

Val

ue

OQASContrast Value

1.04 1.03

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40


SBKPRK

N=25

Con

trast

Val

ue

OQASContrast Value

1.04 1.031.13 1.06 1.04

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40


SBKPRK

N=25

Con

trast

Val

ue

OQASContrast Value

1.04 1.031.13

0.921.06 1.03 1.04

0.96

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40


SBKPRK

N=25

Con

trast

Val

ue

-1%+3%+6%--SBK

-5% 0%-13%--PRK

6 Month3 Month1 MonthPre-Op

Change in MTF Value

OQASResults

-7%-1%-13%--PRK

-1%+2%+8%--SBK6 Month3 Month1 MonthPre-Op

Change in Contrast Value

MTF

MTF

6 month3 month1 monthPre-Op

SBK

PRK

OQAS Sample Point Spread

38.79

39.43

24.51

42.11

35.89

41.67 42.56

36.24

Retinal Image QualityClinical Application of OQAS

Retinal Image QualityNormal Eye

• 33 year old male• BSCVA 20/15

• MTF = 43.58• Contrast Value = 1.48

Retinal Image QualityCortical Cataract

• 62 year old male• BSCVA 20/20-2


Retinal Image QualityNuclear Sclerosis

• 66 year old male• BSCVA 20/25


Conclusion

• Double pass technique can be used to assess theoverall image quality not possible with snellenvisual acuity charts

• At 1 month, the retinal image quality decreasedsignificantly in PRK eyes compared to SBK eyes

• Retinal image quality was higher in all post-opvisits for SBK eyes compared to PRK eyes

• There was a slight decrease in retinal imagequality from 3 month to 6 month in all eyes

• Further study needed on importance of scatter onoverall quality of vision

comparison of retinal image quality between sbk and...

Documents